\section{Conclusion and open questions}
In this paper, we studied the power of token-forwarding algorithms for
gossip in dynamic networks. We showed a lower bound of $\Omega(nk/\log
n)$ rounds for any deterministic online token forwarding algorithm
which matches the known upper bound of $O(nk)$ up to a logarithmic
factor.  This leaves us with an important open question: what is the
complexity of {\em randomized}\/ online token-forwarding algorithms?
In fact, for small token sizes (e.g., $O(\log n)$ bits) even the best
online algorithm we know based on network coding takes $O(nk/\log n)$
rounds~\cite{haeupler+k:dynamic}.  In contrast, we show that in the
offline setting there exist centralized token-forwarding algorithms
that run in $O(n^{1.5}\sqrt{\log n})$ time.  An interesting open
problem is to obtain tight bounds on offline token-forwarding
algorithms.



